
XRT86SH221
PRELIMINARY
77
SDH-TO-PDH FRAMER/MAPPER WITH INTEGRATED 21-CHANNEL E1 SH LIU
REV. P1.0.5
otherwise it is set to "0". Detected errors are tallied in the BIP2CNTx counters that can be read by the
processor in registers BIP2CNT1 to BIP2CNT21
Bit 4 of V5 is used for VT Path Remote Failure Indication (RFI-V). As described in GR-253-CORE, when
automatic RFI-V insertion is enabled by writing "1" to bit VTRFIEN of registers INS1 to INS21, RFI-V will be
signalled by inserting a "1" in the RFI-V bit of byte V5 when LOP-V, AIS-V, UNEQ-V or PLM-V is detected for
more than 2± seconds on the received tributary in the corresponding time slot. The RFI-V signalling is
removed, and bit RFI-V of byte V5 is cleared if the condition that triggered it is absent for 10± seconds.
Bits [3:1] of V5 are used for VT Path Signal Label and indicate the contents of the tributary. Only the following
codes are generated by the tributary generator or expected by the VT PTE:
000 : Unequipped or not provisioned
010 : Asynchronous Mapping of E1
100 : Byte Synchronous Mapping E1
Bit 0 of V5 is used for one-bit VT Path Remote Defect Indication (RDI-V) As described in GR-253-CORE.
When automatic RDI-V insertion is enabled by writing "1" to bit VTRDIEN of registers INS1 to INS21, RDI-V will
be signalled by inserting a "1" in the RDI-V bit of byte V5 when LOP-V, AIS-V, UNEQ-V or PLM-V is detected
on the received tributary in the corresponding time slot.
VC-12 Path Remote Loopback Signaling
Voyager-lite supports in-band signaling within the low-order VC-12 path overhead to request VC-12 path
remote loopback (E1 payloads) provisioning at down-stream equipment. Signaling will be sent on the STM-1
transmit output from the request originating system (sending system) and received on the STM-1 input of the
far-end system (receiving system). Once the receiving system detects this in-band message, a status flag is
set to indicate the remote loopback request detection. The system software will detect this flag through
interrupts and subsequently provision the appropriate low-order path for remote loopback. The sending
system shall continue sending the in-band message until such time that the remote loopback should be
removed. At this time, the VC-12 Path Overhead/Payload content within the STM-1 transmit output of the
sending system shall resume normal function. Upon detecting termination of the remote loopback request, the
receiving equipment shall set a status flag to indicate the clearance of the remote loopback request. The
system software can detect this flag and subsequently remove the remote loopback provisioning for the
appropriate low-order path. This function is provided on a per VC-12 basis.
The LSB of the bit stuff byte immediately following V5 is used as the location for the remote loopback request
messaging. During normal operation, this bit will contain the usual stuff bits. However, during remote loopback
request transmission, this bit shall transmit a continuous, alternating pattern of 1’s and 0’s. The pattern shall
always begin with a "1" and terminate immediately upon release of the software control bit for the remote
loopback request enable. The receiving equipment shall monitor this bit location for the pattern of
"1010101010", or exactly ten bits of alternating 1's and 0's with the first bit having a value of "1". Once the
stated pattern is detected, the receiver sets a status flag indicating detection of the remote loopback request.
This bit should be reset upon read and should not be set again until clearance of the remote loopback request
is detected, and a new remote loopback request message is received.
Detection and cancellation examples:
J2 : VT Path Trace
Byte J2 is used to transmit repetitively a Low Order Path Access Point Identifier so that a path receiving
terminal can verify its continued connection to the intended transmitter. The Path Access Point Identifier
supports both 16-byte and 64-byte frame as the J0 byte defined in the earlier section.
The 64 byte RAM is used on a shared basis with J2 and N2 bytes. When the 64 byte J2 message mode is
configured, the N2 tandem connection feature is disabled. When the J2 message mode is configured as 16
byte, two 16 byte segments are used for TC (tandem connection) and J2.